Light emitting device and lcd backlight using the same

ABSTRACT

The present invention provides a light emitting device which comprises blue and red light emitting diode (LED) chips and at least one phosphor for emitting green light by means of light emitted from the blue LED chip, and an LCD backlight including the light emitting device. According to the light emitting device of the present invention, uniform white light can be implemented and both high luminance and wider color reproduction range can also be obtained. Accordingly, an LCD backlight for uniform light distribution on an LCD as well as low power consumption and high durability can be manufactured using the light emitting device.

RELATED APPLICATIONS

This application is a U.S. national phase application of PCTInternational Application No. PCT/KR2006/003950, filed Sep. 29, 2006,which claims priority of Korean Patent Application No. 10-2006-0021462,filed Mar. 7, 2006, and to Korean Patent Application No. 2005-0092001,filed Sep. 30, 2005, the contents of which are incorporated herein byreference in their entirety.

FIELD OF THE INVENTION

The present invention relates a light emitting device and an LCDbacklight using the light emitting device. More particularly, thepresent invention relates to a light emitting device capable ofimplementing uniform white light and having a wide color reproductionrange, and an LCD backlight using the light emitting device.

BACKGROUND OF THE INVENTION

As high-performance portable information processing devices and mobilecommunication terminals have been continuously required with thedevelopment of information and communication technologies, various kindsof components with high performance and quality have been continuouslyrequired in systems. Liquid crystal displays (LCDs), which have beengenerally applied to monitors of medium- and large-sized terminals suchas notebook computers, require white backlight sources at rear sidethereof. In a case where a cold cathode fluorescent lamp (CCFL) isgenerally used as such a backlight source, there are many advantages inthat uniform white light with high luminance is implemented, and thelike. However, it may be difficult to continuously use the CCFL, becausethe CCFL cannot be further employed due to the future restriction on theuse of mercury. Accordingly, studies on backlight sources with which theCCFLs can be replaced have been actively conducted. Among the backlightsources, a backlight source using a light emitting device has come intothe spotlight as a light source capable of substituting for the CCFLs.

A light emitting diode (LED) refers to a device in which minoritycarriers (electrons or holes) injected by means of a p-n junctionstructure of a semiconductor are produced, and light is emitted due torecombination of the carriers. Since the LED has low power consumptionand long lifespan, can be mounted in a narrow space and has strongresistance against vibration, it has been increasingly employed ascomponents in a variety of information processing and communicationdevices.

As a prior art of an LCD backlight source using a light emitting diode,an LCD backlight source module has been disclosed in Korean PatentLaid-Open Publication No. 2002-0041480, in which blue light emitted froma blue light emitting diode is converted into white light using aphosphor and the white light is then incident onto a light guide platefor the uniform light distribution, so that an LCD can have uniformlight distribution, low power consumption and high durability. In theLCD backlight source module, the blue light emitting diode and phosphorcan be used to implement uniform white light with high luminance.However, since a color reproduction range which can be expressed whenlight is transmitted into RGB color filters is considerably narrow in acase where the LCD backlight source module is used as a white lightsource positioned at the rear of an LCD, there is a limitation in theimplementation of images closer to natural colors. Particularly, sincethe above color reproduction range is greatly lower than the colorreproduction range provided by the National Television System Committee(NTSC), it is difficult to reproduce more realistic colors.

As another prior art, a method of driving an LCD backlight has beendisclosed in Korean Patent Laid-Open Publication No. 2004-0087974, inwhich a single white light emitting diode or three red, blue and greenlight emitting diodes are used in an LCD backlight to form a whitebacklight source, and a microcomputer is used to measure input currentand color of each LED and then to adjust the current supplied finally toeach LED. A backlight source using three red, blue and green lightemitting diodes can satisfy a considerably wide color reproduction rangeas compared with an existing CCFL, but since thermal or temporalcharacteristics of the respective LEDs are different from one another,there are disadvantages in that a color tone is changed depending on ause environment, and particularly, the colors are not uniformly mixeddue to the occurrence of uneven colors, or the like. Further, there areadditional disadvantages in that color coordinates vary due to change inthe output of each chip depending on an ambient temperature, it isdifficult to implement high luminance and a circuit configuration inwhich the driving of each LED chip is considered is complicated.

TECHNICAL PROBLEM

The present invention is conceived to solve the aforementioned problems.Accordingly, an object of the present invention is to provide a lightemitting device capable of implementing uniform white light and havinghigh luminance and a wide color reproduction range.

Another object of the present invention is to provide an LCD backlightwith uniform light distribution on an LCD as well as low powerconsumption and high durability using a light emitting device capable ofimplementing uniform white light and having a wide color reproductionrange.

TECHNICAL SOLUTION

According to an aspect of the present invention for achieving theaforementioned objects, there is provided a light emitting device, whichcomprises at least one blue light emitting diode (LED) chip, at leastone red LED chip, and at least one phosphor for emitting green light bymeans of light emitted from the blue LED chip.

Preferably, the blue LED chip emits light with a wavelength of 430 to500 nm, the red LED chip emits light with a wavelength of 580 to 760 nm,and the phosphor emits light with a wavelength of 500 to 580 nm. Morepreferably, the blue LED chip emits light with a wavelength of 450 to470 nm, the red LED chip emits light with a wavelength of 620 to 640 nm,and the phosphor emits light with a wavelength of 515 to 540 nm.

A silicate- or thiogallate-based phosphor may be used as the phosphor.Moreover, two or more kinds of different phosphors for emitting greenlight may be combined and employed.

The phosphor may include a phosphor expressed as in the followingchemical formula:

<Chemical Formula>

a(M^(I)O)·b(M^(II)O)·c(M^(III)A)·d(M^(III) ₂O)·e(M^(IV) ₂O₃)·f(M^(V)_(o)O_(p))·g(SiO₂)·h(M^(VI) _(x)O_(y))

wherein M^(I) is at least one element selected from the group consistingof Pb and Cu, M^(II) is at least one element selected from the groupconsisting of Be, Mg, Ca, Sr, Ba, Zn, Cd and Mn, M^(III) is at least oneelement selected from the group consisting of Li, Na, K, Rb, Cs, Au andAg, M^(IV) is at least one element selected from the group consisting ofB, Al, Ga and In, M^(V) is at least one element selected from the groupconsisting of Ge, V, Nb, Ta, W, Mo, Ti, Zr and Hf, M^(VI) is at leastone element selected from the group consisting of Bi, Sn, Sb, Sc, Y, La,Ce, Pr, Nd, Pm, Sm, Eu, Gd, Th, Dy, Ho, Er, Tm, Yb and Lu, A is at leastone element selected from the group consisting of F, Cl, Br and I, andwherein a, b, c, d, e, f, g, h, o, p, x and y are set in a range of0<a≦2, 0≦b≦8, 0≦c≦4, 0≦d≦2, 0≦e≦2, 0≦f≦2, 0≦g≦10, 0≦h≦5, 1≦o≦2, 1≦p≦5,1≦x≦2 and 1≦y≦5.

The phosphor may include a phosphor expressed as in the followingchemical formula:

<Chemical Formula>

(A_(1-x-y)Eu_(x)M^(I) _(y))(B_(2-y)M^(II) _(y))S₄

wherein A is at least one element selected from the group consisting ofBa, Sr and Ca, B is at least one element selected from the groupconsisting of Al, Ga and In, M^(I) is at least one rare earth elementselected from the group consisting of Sc, Y, La, Gd and Lu, M^(II) is atleast one element selected from the group consisting of Mg, Zn and Be,and wherein x and y are set in a range of 0.005<x<0.9, 0<y<0.995 andx+y<1.

The phosphor may include a phosphor expressed as in the followingchemical formula:

<Chemical Formula>

(A_(1-x-y)Eu_(x)(M^(I) _(0.5)M^(II) _(0.5))_(y))B₂S₄

wherein A is at least one element selected from the group consisting ofBa, Sr and Ca, B is at least one element selected from the groupconsisting of Al, Ga and In, M^(I) is at least one rare earth elementselected from the group consisting of Sc, Y, La, Gd and Lu, M^(II) is atleast one element selected from the group consisting of Li, Na and K,and wherein x and y are set in a range of 0.005<x<0.9, 0<y<0.995 andx+y<1.

The phosphor may further include a phosphor expressed in at least one ofthe following chemical formulas:

<Chemical Formula>

(2-x-y)SrO·x(Ba_(u),Ca_(v))O·(1-a-b-c-d)SiO₂·aP₂O₅bAl₂O₃cB₂O₃dGeO₂:yEu²⁺

wherein x, y, a, b, c, d, u and v are set in a range of 0≦x<1.6,0.005<y<0.5, x+y≦1.6, 0≦a≦0.5, 0≦b≦0.5, 0≦c≦0.5, 0≦d≦0.5 and u+v=1; and

<Chemical Formula>

(2-x-y)BaO·x(Sr_(u),Ca_(v))O·(1-a-b-c-d)SiO₂·aP₂O₅bAl₂O₃cB₂O₃dGeO₂:yEu²⁺

wherein x, y, u and v are set in a range of 0.01<x<1.6, 0.005<y<0.5,u+v=1 and x·u≧0.4, and at least one value of a, b, c and d is greaterthan 0.01.

The light emitting device of the present invention may further comprisea scattering agent with a size of 0.1 to 20 μm. The scattering agent mayinclude at least one selected from the group consisting of SiO₂, Al₂O₃,TiO₂, Y₂O₃, CaCO₃ and MgO.

The light emitting device of the present invention may further comprisea body with the LED chips mounted thereon, and a molding member which isformed on top of the body to encapsulate the LED chips and contains thephosphor. The body may be a substrate or a heat sink or a lead terminal.

According to another aspect of the present invention, there is providedan LCD backlight comprising the aforementioned light emitting device.

ADVANTAGEOUS EFFECTS

According to the present invention, a white light emitting devicecapable of implementing uniform white light and having high luminanceand a wide color reproduction range can be manufactured by using blueand red light emitting diode chips and a phosphor that emits green lightby means of blue light. In particular, there is an advantage in that alight emitting device of the present invention can be applied to an LCDbacklight due to the implementation of uniform light and a superiorwhite light emitting characteristic with a wide color reproductionrange.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing a first embodiment of a lightemitting device according to the present invention.

FIG. 2 is a sectional view showing a second embodiment of the lightemitting device according to the present invention.

FIG. 3 is a sectional view showing a third embodiment of the lightemitting device according to the present invention.

FIG. 4 is a sectional view showing a fourth embodiment of the lightemitting device according to the present invention.

FIG. 5 is a sectional view showing a fifth embodiment of the lightemitting device according to the present invention.

FIG. 6 is a graph illustrating the excitation and emission spectra of asilicate phosphor applied to the present invention.

FIG. 7 is a graph illustrating the excitation and emission spectra of athiogallate phosphor applied to the present invention.

FIG. 8 is a graph illustrating emission spectra of a light emittingdevice comprising blue and red light emitting diode chips and a silicatephosphor together with the transmittance of a general RGB color filter.

FIG. 9 is a graph illustrating emission spectra of a light emittingdevice comprising blue and red light emitting diode chips and athiogallate phosphor together with the transmittance of a general RGBcolor filter.

FIG. 10 is a graph illustrating a color reproduction range of a lightemitting device according to the present invention after a white lightsource has been transmitted into a filter.

DETAILED DESCRIPTION

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings.However, the present invention is not limited to the embodiments setforth herein but can be implemented in different forms. Rather, thepreferred embodiments are merely provided to allow the present inventionto be completely described herein and to fully convey the scope of theinvention to those skilled in the art. In the drawings, like elementsare designated by the same reference numerals.

A light emitting device according to the present invention comprisesblue and red light emitting diode (LED) chips and at least one or morephosphors each emitting green light using a portion of blue light as anexcitation source such that white light can be obtained from thecombination of blue and red light emission from the LED chips and greenlight emission from the phosphors. That is, white light can beimplemented through the combination of a blue LED chip that emits lightwith a wavelength of 430 to 500 nm, a red LED chip that emits light witha wavelength of 580 to 760 nm, and a phosphor that can produce greenlight with a wavelength of 500 to 580 nm using blue light as anexcitation source. More preferably, the light emitting device accordingto the present invention comprises the combination of a blue LED chipthat emits light with a wavelength of 450 to 470 nm, a red LED chip thatemits light with a wavelength of 620 to 640 nm, and a phosphor that canproduce green light with a wavelength of 515 to 540 nm using the bluelight as an excitation source. A silicate- or thiogallate-based phosphormay be used as the phosphor that is excited by blue light and emitsgreen light. Moreover, two or more kinds of different phosphors may beemployed in a state where they are mixed with one another.

The silicate-based phosphor has a structure as expressed in thefollowing chemical formula of chemistry FIG. 1:

[Chemistry FIG. 1]

a(M^(I)O)·b(M^(II)O)·c(M^(III)A)·d(M^(III) ₂O)·e(M^(IV) ₂O₃)·f(M^(V)_(o)O_(p))·g(SiO₂)·h(M^(VI) _(x)O_(y))

In the chemistry FIG. 1, M^(I) is at least one element selected from thegroup consisting of Pb and Cu; M^(II) is at least one element selectedfrom the group consisting of Be, Mg, Ca, Sr, Ba, Zn, Cd and Mn; M^(III)is at least one element selected from the group consisting of Li, Na, K,Rb, Cs, Au and Ag; M^(IV) is at least one element selected from thegroup consisting of B, Al, Ga and In; M^(V) is at least one elementselected from the group consisting of Ge, V, Nb, Ta, W, Mo, Ti, Zr andHf; M^(VI) is at least one element selected from the group consisting ofBi, Sn, Sb, Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm,Yb and Lu; A is at least one element selected from the group consistingof F, Cl, Br and I.

Further, in the chemistry FIG. 1, a, b, c, d, e, f, g, h, o, p, x and yare set in a range of 0≦a≦2, 0≦b≦8, 0≦c≦4, 0≦d≦2, 0≦e≦2, 0≦g≦10, 0≦h≦5,1≦o≦2, 1≦p≦5, 1≦x≦2 and 1≦y≦5.

Tables 1 and 2 illustrate an effect when the silicate-based phosphorhaving a structure as chemistry FIG. 1 contains copper.

Table 1 shows the changes in zeta potential and mobility between aphosphor containing no copper and other phosphors containing copper withdifferent concentrations, and Table 2 shows relative intensities withrespect to time of compounds containing copper and a compound containingno copper under a temperature of 85° C. and a relative humidity of 100%.

TABLE 1 Phosphor Composition Zeta Potential Mobility (Ca,Sr,Ba,Eu)—SiO₄containing −3.5 mV −2.4 · 10⁻⁵ cm²/Vs no copper (Ca,Sr,Ba,Eu)—SiO₄containing −3.3 mV −2.3 · 10⁻⁵ cm²/Vs 0.005 mol of copper(Ca,Sr,Ba,Eu)—SiO₄ containing −2.5 mV −1.8 · 10⁻⁵ cm²/Vs 0.01 mol ofcopper (Ca,Sr,Ba,Eu)—SiO₄ containing +0.33 mV  −1.4 · 10⁻⁵ cm²/Vs 0.1mol of copper

TABLE 2 Relative Relative Relative Relative Relative Intensity IntensityIntensity Intensity Intensity after 24 after 100 after 200 after 500after 1000 Phosphor composition hours hours hours hours hours(Ca,Sr,Ba,Eu)—SiO₄ containing 98.3 96.0 93.3 84.7 79.3 no copper(Ca,Sr,Ba,Eu)—SiO₄ containing 100.0 99.6 98.6 96.3 94.0 0.005 mol ofcopper (Ca,Sr,Ba,Eu)—SiO₄ containing 98.6 98.5 95.8 92.8 90.1 0.01 molof copper (Ca,Sr,Ba,Eu)—SiO₄ containing 98.7 98.0 96.4 93.2 90.0 0.1 molof copper

Referring to Tables 1 and 2, the stability against water of the compoundcontaining copper is much higher than that of the compound containing nocopper. Thus, the silicate-based phosphor containing copper has animproved stability against water, moisture and a polar solvent. In acase where the silicate-based phosphor is applied to light emittingdevices or LCD backlights under the above environment, it can providesuperior reliability.

The thiogallate-based phosphor has a structure as expressed in thefollowing chemical formula of chemistry FIG. 2:

[Chemistry FIG. 2]

(A_(1-x-y)Eu_(x)M^(I) _(y))(B_(2-y)M^(II) _(y))S₄

In the chemistry FIG. 2, A is at least one element selected from thegroup consisting of Ba, Sr and Ca; B is at least one element selectedfrom the group consisting of Al, Ga and In; M^(I) is at least one rareearth element selected from the group consisting of Sc, Y, La, Gd andLu; M^(II) is at least one element selected from the group consisting ofMg, Zn and Be. Further, in the chemistry FIG. 2, x and y are set in arange of 0.005<x<0.9, 0<y<0.995 and x+y≦1. Since the same amounts ofM^(I) and M^(II) are substituted at positions A and B, respectively, acharge balance is accomplished. Particularly, M^(I) and M^(II) can beselected to have ion radiuses similar to those of elements at A and Bpositions, respectively. Accordingly, since the crystal field amplitudeof active ions is not changed, the light emitting efficiency can beincreased while maintaining the emission wavelength of a phosphor with acomposition before substitution.

Further, the chemical formula of the thiogallate-based phosphor has astructure as the following chemical formula of chemistry FIG. 3:

[Chemistry FIG. 3]

(A_(1-x-y)Eu_(x)(M^(I) _(0.5)M^(II) _(0.5))_(y))B₂S₄

In the chemistry FIG. 3, A is at least one element selected from thegroup consisting of Ba, Sr and Ca; B is at least one element selectedfrom the group consisting of Al, Ga and In; M^(I) is at least one rareearth element selected from the group consisting of Sc, Y, La, Gd andLu; M^(II) is at least one element selected from the group consisting ofLi, Na and K. Further, x and y are set in a range of 0.005<x<0.9,0<y<0.995 and x+y≦1.

In the thiogallate-based phosphor having a structure as expressed in thechemistry FIG. 3, a position A required for a divalent ion is firstreplaced with a trivalent ion having a similar ion size and thensimilarly replaced with a monovalent ion having a similar ion size atthe same amount of the trivalent ion in order to compensate for thecharge unbalance due to the replacement with the trivalent ion. Thus, asuperior emission characteristic can be obtained while the entire chargebalance is kept at the position A required for a divalent ion.

That is, in the thiogallate-based phosphor having a structure asexpressed in the chemistry FIG. 3, i.e. in the general formula of thethiogallate phosphor AB₂S₄, a position A required for a divalent ion isfirst replaced with a trivalent M^(II) having a similar ion size andthen similarly replaced with a monovalent M^(I) having a similar ionsize at the same amount of the trivalent M^(II) in order to compensatefor the charge unbalance due to the replacement with the trivalent ion.Thus, a superior emission characteristic can be obtained while theentire charge balance is kept at the position A required for a divalention.

Consequently, since the replacement of ions having the same size isconsidered in such a double replacement, the thiogallate-based phosphorhaving a structure as expressed in the chemistry FIG. 3 can maintain thesame charge balance as the existing thiogallate phosphor while notcausing the crystal lattice distortion. Accordingly, thethiogallate-based phosphor has superior emission efficiency and luminousintensity while maintaining the entire charge balance.

Moreover, a YAG-based phosphor is further included with the silicate- orthiogallate-based phosphor such that much superior green light can beimplemented under the excitation in a blue wavelength band.

The above YAG-based phosphor has a structure as expressed in thefollowing chemical formula of chemistry FIG. 4:

[Chemistry FIG. 4]

(Re_(1-r)Sm_(r))₃(Al₁₋₃Ga_(s))₅O₁₂:Ce

In the chemistry FIG. 4, Re is at least one element selected from thegroup consisting of Y and Gd. Further, in the chemistry FIG. 4, r and sare set in a range of 0≦r<1 and 0≦s≦1.

In addition, the phosphor has a structure as expressed in the followingchemical formula of chemistry FIG. 5:

[Chemistry FIG. 5]

M^(I) _(a)M^(II) _(b)M^(III) _(c)O_(d)

In the chemistry FIG. 5, M^(I) is at least Ce and at least one elementselected from the group consisting of Cr, Mn, Fe, Co, Ni, Cu, Pr, Nd,Sm, Eu, Tb, Dy, Ho, Er, Tm and Tb; M^(II) is at least one elementselected from the group consisting of Mg, Ca, Zn, Sr, Cd and Ba; andM^(III) is at least one element selected from the group consisting ofAl, Sc, Ga, Y, In, La, Gd and Lu. Further, in the chemistry FIG. 5, a,b, c and d are set in a range of 0.0001≦a=0.2, 0.8≦b≦1.2, 1.6≦c≦2.4 and3.2≦d≦4.8.

In addition, the phosphor has a structure as expressed in the followingchemical formula of chemistry FIG. 6:

[Chemistry FIG. 6]

(Sr_(1-u-v-x)Mg_(u)Ca_(v)Ba_(x))(Ga_(2-y-z)Al_(y)In_(z)S₄):Eu²⁺

In the chemistry FIG. 6, u, v, x, y and z are set in a range of 0≦u≦1,0≦v≦1, 0≦x≦1, 0≦(u+v+x)≦1, 0≦y≦2, 0≦z≦2 and 0≦y+z≦2.

Furthermore, the phosphor has a structure as expressed in the followingchemical formula of chemistry FIG. 7:

[Chemistry FIG. 7]

(2-x-y)SrO·x(Ba_(u),Ca_(v))O·(1-a-b-c-d)SiO₂·aP₂O₅bAl₂O₃cB₂O₃dGeO₂:yEu²⁺

In the chemistry FIG. 7, x, y, a, b, c, d, u and v are set in a range of0≦x<1.6, 0.005<y<0.5, x+y≦1.6, 0≦a≦0.5, 0≦b≦0.5, 0≦c≦0.5, 0≦d≦0.5 andu+v=1.

In addition, the phosphor has a structure as expressed in the followingchemical formula of chemistry FIG. 8: [Chemistry FIG. 8]

(2-x-y)BaO·x(Sr_(u),Ca_(v))O·(1-a-b-c-d)SiO₂·aP_(s)O₅bAl₂O₃cB₂O₃dGeO₂:yEu²⁺

In the chemistry FIG. 8, x, y, u and v are set in a range of 0.01<x<1.6,0.005<y<0.5, u+v=1 and x·u≧0.4; and at least one value of a, b, c and dis greater than 0.01.

Accordingly, the light emitting device of the present invention has theblue and red LED chips and the aforementioned phosphor, and thus, whitelight can be implemented through the combination of the lights emittedfrom the chips and the phosphor. That is, blue and red light emittedfrom the LED chips and green light wavelength-converted by the phosphorare mixed to implement the white light. Since a spectrum area in a greenregion with higher visibility is considerably increased as compared within a case where a conventional three-color LED of red, blue and green isused, the white light emitting device of the present invention canobtain high luminescence. Further, there is an advantage in that thewhite light emitting device of the present invention can have a widercolor reproduction range as compared with in a case where a conventionalblue LED and a phosphor are used. Therefore, a light emitting device ofthe present invention can be employed to an LCD backlight as a superiorlight source due to its enhanced characteristics of high luminance andwide color reproduction range. In particular, a thiogallate-basedphosphor has a relatively narrow bandwidth, i.e. a bandwidth of anemission spectrum measured at a ½ peak intensity. Accordingly, a lightemitting device employing a thiogallate-based phosphor with a narrowbandwidth can be used as a light source of an LCD backlight to enhancethe color reproduction of LCDs.

Hereinafter, a light emitting device of the present invention will bedescribed with reference to the accompanying drawings.

FIG. 1 is a sectional view showing a first embodiment of a lightemitting device according to the present invention.

Referring to this figure, the light emitting device comprises asubstrate 10; electrodes 30, 40 and 50 formed on the substrate 10; andLED chips 20 and 25 that emit blue and red light, respectively. Amolding member 60 for encapsulating the LED chips 20 and 25 is furtherformed on top of the substrate, and the aforementioned phosphor 70 iscontained in the interior of the molding member 60.

The substrate 10 may include a reflective portion (not shown)manufactured by forming a predetermined groove in a central region ofthe substrate 10 and then allowing a sidewall of the groove to beinclined at a predetermined slope. Such a reflective portion is formedsuch that the reflection of light emitted from the LED chips 20 and 25can be maximized and emission efficiency can also be enhanced.

The electrodes of this embodiment include first, second and thirdelectrodes 30, 40 and 50 which may be formed on the substrate 10 using aprinting technique or an adhesive.

The blue and red LED chips 20 and 25, each of which has positive andnegative electrodes on top and bottom planes thereof, are commonlymounted on the second electrode 40 and are connected electrically to thefirst and third electrodes 30 and 50 through wires 90, respectively, sothat the respective LED chips 20 and 25 can be driven simultaneously orindependently.

The shape and number of the electrodes 30, 40 and 50 or the resultantmounting configuration of the LED chips 20 and 25 is not limited to theaforementioned description but can be implemented in various ways. Forexample, the blue and red LED chips, each of which has both of thepositive and negative electrodes on a top plane thereof, may be mounted.

Further, the molding member 60 for encapsulating the LED chips 20 and 25is formed on top of the substrate 10. The phosphor 70 that emits greenlight using blue light as an excitation source is included in themolding member 60. As described above, a silicate- or thiogallate-basedphosphor may be used as the phosphor 70, and a variety of phosphors maybe mixed and then used. As shown in this figure, it is preferred thatthe phosphors 70 be uniformly distributed in the interior of the moldingmember 60. Alternatively, after a mixture of the phosphor 70 and resinhas been dotted at a predetermined thickness to surround top and sidesurfaces of the blue LED chip 20, the molding member 60 may be formed.

In this embodiment, light emitted from the blue and red LED chips 20 and25 are uniformly mixed due to the phosphors 70 evenly distributed in themolding member 60, so that more uniform white light can be implemented.

The molding member 60 may be formed through an injecting process using amixture of a predetermined epoxy resin and the phosphors 70. Further,the molding member 60 may be formed in such a manner that it is firstmanufactured using an additional mold and then pressed or heat-treated.The molding member 60 may be shaped into an optical lens form, a flatplate form, a form with a predetermined irregularity on a surfacethereof, and the like.

In such a light emitting device of the present invention, primary lightis emitted from the blue and red LED chips 20 and 25, and a portion ofthe primary light excites the phosphor 70 to emit wavelength-convertedsecondary light, so that a color within a desired spectrum range can beimplemented by means of the mixture of the primary and secondary light.That is, blue and red light is emitted from the blue and red LED chips20 and 25, respectively, and green light is emitted from the phosphor 70that is excited by a portion of the blue light. Therefore, a portion ofblue light and red light serving as the primary light, and green lightserving as the secondary light are mixed with one another such thatwhite light can be implemented.

FIG. 2 is a sectional view showing a second embodiment of the lightemitting device according to the present invention.

Referring to this figure, the light emitting device comprises asubstrate 10; electrodes 30 and 40 formed on the substrate 10; and LEDchips 20 and 25 that emit blue and red light, respectively. A moldingmember 60 for encapsulating the LED chips 20 and 25 is further formed ontop of the substrate 10, and the aforementioned phosphor 70 and ascattering agent 80 are contained in the interior of the molding member60. The configuration of the light emitting device according to thesecond embodiment is almost identical with that of the first embodiment,and thus, detailed descriptions overlapping with the first embodimentwill be omitted herein.

The electrodes of the second embodiment are formed to include a firstelectrode 30, a second electrode 40 and a third electrode (not shown).The LED chips 20 and 25 are mounted on the first and second electrode 30and 40, respectively, and then are commonly connected electrically tothe third electrode (not shown) through wires 90. Further, first, secondthird and fourth electrodes may be provided such that the LED chips 20and 25 are mounted on the first and second electrodes 30 and 40,respectively, and are independently connected electrically to the thirdand fourth electrode (not shown) through wires 90.

In addition, the molding member 60 for encapsulating the LED chips 20and 25 is further formed on top of the substrate 10. The phosphor 70 andthe scattering agent 80 are evenly distributed are contained in themolding member 60. As described above, the phosphor used herein mayinclude the phosphor 70, i.e. a silicate or thiogallate-based phosphor,which emits green light using blue light as an excitation source.Moreover, two or more kinds of different phosphors may be mixed and thenemployed. For example, a YAG-based phosphor may be further contained. Inaddition, the scattering agent 80 is added such to facilitate mixing thelight, and has a particle size of 0.1 to 20 μm. At least one of SiO₂,Al₂O₃, TiO₂, Y₂O₃, CaCO₃ and MgO is used as the scattering agent 80.

As such, since the light emitting device containing the scattering agent80 allows light emitted from the LED chips 20 and 25 to be scattered bythe scattering agent 80 and then emitted to the outside, light can beuniformly emitted in a wide range without forming an unnecessary lightemitting pattern. Accordingly, lights with different wavelengths areemitted in a wide range and then mixed more uniformly, and consequently,the light emitting device can implement uniform white light.

FIG. 3 is a sectional view showing a third embodiment of the lightemitting device according to the present invention.

Referring to this figure, the light emitting device comprises asubstrate 10; electrodes 30 and 40 formed on the substrate 10; and LEDchips 20 and 25 that emit blue and red light, respectively. Theconfiguration of the third embodiment is almost identical with that ofthe second embodiment, and detailed descriptions overlapping with thesecond embodiment will be omitted herein. Alternatively, the lightemitting device comprises first and second molding members 61 and 62formed on top of the substrate 10. The phosphors 70 are uniformlydistributed in the first molding member 61 to encapsulate the LED chips20 and 25, and the scattering agents 80 are uniformly distributed in thesecond molding member 62 to surround the first molding member 61.

Blue and red light is emitted from the blue and red LED chips 20 and 25,respectively, and a portion of the blue light excites the phosphor 70 toemit green light while the blue and red light passes through the firstmolding member 61. Therefore, a portion of the blue light, the red lightand the wavelength-converted green light are mixed with one another toimplement white light. At this time, light with different wavelengths ismore uniformly mixed by the scattering agent 80 distributed in thesecond molding member 62, and thus, the light emitting device canimplement uniform white light.

Although it is illustrated in this figure that the first molding member61 with the phosphors 70 contained therein is formed to encapsulate theblue and red LED chips 20 and 25, the present invention is not limitedthereto. That is, after the first molding member 61 is formed toencapsulate the blue LED chip 20, the second molding member 62 with thescattering agents 80 uniformly distributed therein may be formed tosurround the first molding member 61 and the red LED chip 25.

FIG. 4 is a sectional view showing a fourth embodiment of the lightemitting device according to the present invention.

Referring to this figure, the light emitting device comprises asubstrate 10; electrodes 30, 40 and 50 formed on the substrate 10; andLED chips 20 and 25 that emit blue and red light, respectively. Theconfiguration of the fourth embodiment is almost identical with that ofthe first embodiment, and thus, detailed descriptions overlapping withthe first embodiment will be replaced with the descriptionscorresponding to FIG. 1. Alternatively, this embodiment furthercomprises a reflector 110 formed on top of the substrate 10 to surroundthe LED chips 20 and 25, and a molding member 60 for encapsulating theLED chips 20 and 25 mounted in a central hole of the reflector 110 isfurther included. The phosphors 70 are evenly distributed and containedin the interior of the molding member 60.

To enhance luminance and light-gathering capacity, an inner wall of thereflector that surrounds the LED chips 20 and 25 may be inclined at apredetermined slope. This is preferably to maximize the reflection oflight emitted from the LED chips 20 and 25 and to enhance the emissionefficiency.

FIG. 5 is a sectional view showing a fifth embodiment of the lightemitting device according to the present invention.

Referring to this figure, the light emitting device comprises a housing100 with first and third electrodes 30 and 50 formed respectively atboth sides thereof and a through-hole formed at the center thereof; asubstrate 15 mounted into the through-hole of the housing 100; and blueand red LED chips 20 and 25 that are commonly mounted on a secondelectrode 40 formed on the substrate 15. At this time, the substrate 15is manufactured as a heat sink using a material with superior thermalconductivity such that heat released from the LED chips 20 and 25 can bemore effectively discharged to the outside. A molding member 60 forencapsulating the LED chips 20 and 25 is further included, and theaforementioned phosphors 70 are uniformly mixed and distributed in themolding member 60. Detailed descriptions overlapping with the first tofourth embodiments will be omitted herein.

As described above, the present invention can be applied to productswith various structures, and is not limited to the aforementionedembodiments. That is, various modifications and changes can be madethereto. In a case of a lamp-type light emitting device, for example, awhite light emitting device of the present invention may be manufacturedby mounting blue and red LED chips on a lead terminal and then forming amolding member with a phosphor uniformly distributed therein asdescribed above. Further, although one blue LED chip and one red LEDchip are used in the aforementioned embodiments, a plurality of blue andred chips may be configured in accordance with the purpose.

FIGS. 6 and 7 are graphs illustrating the excitation and emissionspectra of silicate and thiogallate phosphors applied to the presentinvention, respectively. As shown in the figures, each of the silicateand thiogallate phosphors absorbs a portion of energy of blue light andexhibits a superior emission spectrum of 510 to 560 nm.

FIG. 8 is a graph illustrating emission spectra of a light emittingdevice comprising blue and red light emitting diode chips and a silicatephosphor together with the transmittance of a general RGB color filter.Further, FIG. 9 is a graph illustrating emission spectra of a lightemitting device comprising blue and red light emitting diode chips and athiogallate phosphor together with the transmittance of a general RGBcolor filter. As shown in the figures, since the light emitting deviceof the present invention has a wider color reproduction range that canbe expressed when light transmits the RGB color filter, there is anadvantage in that images close to natural colors can be implemented.

FIG. 10 is a graph illustrating a color reproduction range of whitelight from a light emitting device after it has been transmitted into afilter according to the present invention. Color implementation can bemade within an area of 72% as compared with the NTSC when a conventionalCCFL is used, while an improved color reproduction range of 94 to 100%over the NTSC can be obtained when the light emitting device of thepresent invention is used.

As described above, a light emitting device of the present invention canbe applied to an LCD backlight because of its high luminance and broadcolor reproduction range characteristics. That is, a general LCDrequires a white backlight source. Since a white light emitting deviceof the present invention exhibits superior luminance and colorreproduction characteristics, it can play a very important role in thedevelopment of LCDs.

While the present invention has been described in connection with thepreferred embodiments, it will be understood by those skilled in the artthat various modifications and changes can be made thereto withoutdeparting from the spirit and scope of the invention defined by theappended claims.

For example, it has been described in the aforementioned embodimentsthat a silicate or thiogallate phosphor is used as a phosphor that isexcited by blue light to emit green light. However, two or more kinds ofphosphors selected among phosphors that are excited by blue light toemit green light may be combined and employed in various ways. Moreover,YAG-based phosphors may be further included.

1. A light emitting device, comprising: at least one blue light emittingdiode (LED) chip; at least one red LED chip; and at least one phosphorfor emitting green light by means of light emitted from the blue LEDchip, wherein the phosphor includes at least one of phosphors expressedas in the following chemical formulas: <Chemical Formula>a(M^(I)O)·b(M^(II)O)·c(M^(III)A)·d(M^(III) ₂O)·e(M^(IV) ₂O₃)·f(M^(V)_(o)O_(p))·g(SiO₂)·h(M^(VI) _(x)O_(y)) wherein M^(I) is at least oneelement selected from the group consisting of Pb and Cu, M^(II) is atleast one element selected from the group consisting of Be, Mg, Ca, Sr,Ba, Zn, Cd and Mn, M^(III) is at least one element selected from thegroup consisting of Li, Na, K, Rb, Cs, Au and Ag, M^(IV) is at least oneelement selected from the group consisting of B, Al, Ga and In, M^(V) isat least one element selected from the group consisting of Ge, V, Nb,Ta, W, Mo, Ti, Zr and Hf, M^(VI) is at least one element selected fromthe group consisting of Bi, Sn, Sb, Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu,Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, A is at least one element selectedfrom the group consisting of F, Cl, Br and I, and wherein a, b, c, d, e,f, g, h, o, p, x and y are set in a range of 0≦a≦2, 0≦b≦8, 0≦c≦4, 0≦d≦2,0≦e≦2, 0≦f≦2, 0≦g≦10, 0≦h≦5, 1≦o≦2, 1≦p≦5, 1≦x≦2 and 1≦y≦5; <ChemicalFormula>(A_(1-x-y)Eu_(x)M^(I) _(y))(B_(2-y)M^(II) _(y))S₄ wherein A is at leastone element selected from the group consisting of Ba, Sr and Ca, B is atleast one element selected from the group consisting of Al, Ga and In,M^(I) is at least one rare earth element selected from the groupconsisting of Sc, Y, La, Gd and Lu, M^(II) is at least one elementselected from the group consisting of Mg, Zn and Be, and wherein x and yare set in a range of 0.005<x<0.9, 0<y<0.995 and x+y<1; and <ChemicalFormula>(A_(1-x-y)Eu_(x))(M^(I) _(0.5)M^(II) _(0.5))_(y))B₂S₄ wherein A is atleast one element selected from the group consisting of Ba, Sr and Ca, Bis at least one element selected from the group consisting of Al, Ga andIn, M^(I) is at least one rare earth element selected from the groupconsisting of Sc, Y, La, Gd and Lu, M^(II) is at least one elementselected from the group consisting of Li, Na and K, and wherein x and yare set in a range of 0.005<x<0.9, 0<y<0.995 and x+y<1.
 2. The lightemitting device as claimed in claim 1, wherein the blue LED chip emitslight with a wavelength of 430 to 500 nm, the red LED chip emits lightwith a wavelength of 580 to 760 nm, and the phosphor emits light with awavelength of 500 to 580 nm.
 3. The light emitting device as claimed inclaim 2, wherein the blue LED chip emits light with a wavelength of 450to 470 nm, the red LED chip emits light with a wavelength of 620 to 640nm, and the phosphor emits light with a wavelength of 515 to 540 nm. 4.The light emitting device as claimed in claim 1, wherein the phosphorfurther includes a phosphor expressed in at least one of the followingchemical formulas: <Chemical Formula>(2-x-y)SrO·x(Ba_(u),Ca_(v))O·(1-a-b-c-d)SiO₂·aP₂O₅bAl₂O₃cB₂O₃dGeO₂:yEu²⁺ wherein x, y, a, b,c, d, u and v are set in a range of 0≦x≦1.6, 0.005≦y≦0.5, x+y≦1.6,0≦a≦0.5, 0≦b≦0.5, 0≦c≦0.5, 0≦d≦0.5 and u+v=1; and <Chemical Formula>(2-x-y)BaO·x(Sr_(u),Ca_(v))O·(1-a-b-c-d)SiO₂·aP₂O₅bAl₂O₃cB₂O₃dGeO₂:yEu²⁺ wherein x, y, u andv are set in a range of 0.01<x<1.6, 0.005<y<0.5, u+v=1 and x·u≧0.4, andat least one value of a, b, c and d is greater than 0.01.
 5. The lightemitting device as claimed in claim 1, further comprising a scatteringagent with a size of 0.1 to 20□.
 6. The light emitting device as claimedin claim 5, wherein the scattering agent is at least one selected fromthe group consisting of SiO₂, Al₂O₃, TiO₂, Y₂O₃, CaCO₃ and MgO.
 7. Thelight emitting device as claimed in claim 1, further comprising: a bodywith the LED chips mounted thereon; and a molding member formed on topof the body to encapsulate the LED chips, wherein the molding membercontains the phosphor.
 8. The light emitting device as claimed in claim7, wherein the body is a substrate or a heat sink or a lead terminal. 9.An LCD backlight comprising a light emitting device according to claim1.